The wings of an airplane have an angle of incidence which is generally not controllable along their profile, whereas, the blades of helicopters and of certain propellers have a variable pitch of which the variations may be controlled but which remain constant along the profile of the blade (only varying the same angle over the entire span). As is well known, it is not possible under such conditions to benefit from an optimum aerodynamic efficiency over the length of the profile for very different working conditions, and the determination of the contours is made for achieving the best compromise in each application. This deficiency is a particularly serious inconvenience for "beating wing" airplanes in which the wings pass through a cycle of very different aerodynamic conditions. The principle of these airplanes is now well known, but they have not been particularly well developed in practice because of this type of problem.
French Pat. Nos. 1,368,710 and 1,430,071 propose a propeller with variable overall pitch which, in order to control the angle, may undergo weak corrections of different amplitude according to the sections of the contour in order to reduce the incident angle of sections of the profile near the hub. This propeller is divided along its length into several sectors, each mounted with a certain play between two stops: the corrections are carried out completely or not at all at the point of each sector by means of a fluid which exerts upon the sector under consideration a pressure causing it, at the end of the angle control, to return to the rear over a small course of travel against the surface of the corresponding stop. However, the same principle of this propeller limits the corrections possible to very slight amplitudes and does not permit obtaining, over different conditions, an angle over the profile close to the optimum angle. For example, for aircraft with beating wings, it would not be possible with this principle to continuously and progressively control the angular position of the various sectors of the wing as a function of the position of the wing in the beating cycle.